The subject matter disclosed herein relates to a three point harmonic drive and, more particularly, to a three point harmonic drive of an electric machine.
Harmonic drive gears are strain wave gears that can improve certain characteristics compared to traditional gearing systems. The advantages of harmonic drive gears include no backlash, compactness and light weight, high gear ratios, reconfigurable ratios within a standard housing, good resolution and excellent repeatability when repositioning inertial loads, high torque capability and coaxial input and output shafts. High gear reduction ratios are possible in a small volume (a ratio from 30:1 up to 320:1 is possible in the same space in which planetary gears typically only produce a 10:1 ratio). Harmonic drive gears are typically used in industrial motion control, machine tool, printing machine, robotics and aerospace for gear reduction but may also be used to increase rotational speed, or for differential gearing.
A typical harmonic drive contains a wave generator with a two point contact arrangement. Normally, this structure is provided to increase the gear ratio of the harmonic drive. However, two point arrangements are unstable radially and require additional bearings to support the radial alignment.